/*
 * Copyright (c) 2012 Johan Fylling
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy 
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights 
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 
 * copies of the Software, and to permit persons to whom the Software is 
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in 
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN 
 * THE SOFTWARE.
 */

part of engine;


class DistanceConstraint implements Constraint {
  final Particle _particleA;
  final Particle _particleB;
  num            _distance;
  
  DistanceConstraint (Particle this._particleA, 
                      Particle this._particleB) {
    fix();
  }
  
  num get distance => this._distance;
  
  Vector2 get endA => this._particleA.position;
  
  Vector2 get endB => this._particleB.position;
  
  /** Fix the constraint's distance to the current particle distance. */
  void fix () {
    Vector2 delta = this._particleA.position - this._particleB.position;
    this._distance = delta.length;
  }
  
  void satisfy () {
    if (this._particleA == null ||
        this._particleB == null) {
      return;
    }
    
    Vector2 delta = this._particleA.position - this._particleB.position;
    num deltaLength = delta.length;
    num diff = (deltaLength - this._distance) * 0.5;
    this._particleA.position = (this._particleA.position - (delta.normalized() * diff));
    this._particleB.position = (this._particleB.position + (delta.normalized() * diff));
  }
}
